As related in the '312 application, isobutene is widely used for the production of a variety of industrially important products, such as butyl rubber for example. Isobutene has been produced commercially to date through the catalytic or steam cracking of fossil feedstocks, and the development of a commercially viable process for the manufacture of isobutene from a renewable source-based feedstock has accordingly become of great interest as fossil resources are increasingly depleted and/or have become more costly to use—especially in consideration of increased demand for isobutene.
Previous to the earlier WO '784 application, a hard-template method had been described for synthesizing ZnxZryOz mixed oxides for the direct and high yield conversion of ethanol (from the fermentation of carbohydrates from renewable source materials, including biomass) to isobutene, wherein ZnO was added to ZrO2 to selective passivate zirconia's strong Lewis acidic sites and weaken Brönsted acidic sites while simultaneously introducing basicity. The objectives of the hard template method were to suppress ethanol dehydration and acetone polymerization, while enabling a surface basic site-catalyzed ethanol dehydrogenation to acetaldehyde, an acetaldehyde to acetone conversion via aldol-condensation/dehydrogenation, and a Brönsted and Lewis acidic/basic site-catalyzed acetone-to-isobutene reaction pathway.
High isobutene yields were in fact realized, but unfortunately, as later experienced by Mizuno et al. (Mizuno et al., “One-path and Selective Conversion of Ethanol to Propene on Scandium-modified Indium Oxide Catalysts”, Chem. Lett. vol. 41, pp. 892-894 (2012)) in their efforts to produce propylene from ethanol, it was found that further improvements in the catalyst's stability were needed.
The WO '784 application concerned the discovery that these improvements could be realized without adding modifying metals and without a reduction in the initial high activity (100 percent ethanol conversion) that had been observed in these mixed oxide catalysts, while the '312 application concerned the further discovery that the mixed oxide catalysts we had been evaluating for converting ethanol to isobutene are also able to catalyze the conversion of acetic acid to isobutene. Since acetic acid can be made by a variety of methods from a number of different starting materials, the capability of these mixed oxide catalysts to catalyze the conversion of acetic acid to isobutene enabled a range of options for utilizing renewable resources more efficiently, all as described in greater detail in the '312 application.
Separately, while commercial production of propionic acid to date has been entirely by petrochemical routes, a variety of proposed fermentation methods have been evaluated from as early as about 1920 for the industrial production of propionic acid, see Playne, “Propionic and Butyric Acids”, Comprehensive Biotechnology: The Principles, Applications and Regulations of Biotechnology in Industry, Agriculture and Medicine, Volume 3, Pergamon Press, New York, N.Y. (1985) at pages 731-759, now incorporated by reference herein. One reason given by Playne for the absence of a commercial fermentation route to propionic acid is that acetic acid has been produced as a significant co-product. Bacteria listed by Playne as of “major importance” for the production of propionic acid from sugars, lactose or lactate through a dicarboxylic acid or acrylic acid metabolic pathway include Propioibacterium, especially P. shermanii; Veillonella paroula; Veillonella alcalescens; Selenomonas ruminantium (ph 5); Selenomonas sputigena (pH 5); Clostridium propionicion Clostridium nomyi; Megasphaera elsdenii (pH 4-8); Bacteriodes fragilis; Bacteriodes riominicola; and Fusobacterium necrophoruni. 
Efforts to produce propionic acid by fermentation methods have continued in recent years, various approaches being described for producing propionic acid as well as some acetic acid in greater and lesser proportions from glucose, lactose, sucrose, xylose, fructose, maltose and lactate substrates. References describing these efforts include WO 2012/064883 to Yang et. al. (describing metabolically engineered organisms for producing propionic acid with increased yield and productivity, and increased tolerance to propionic acid and acidic pHs); Lewis and Yang, “Propionic acid fermentation by Propionibacterium acidipropionici: effect of growth substrate”, Appl. Microbiol. Biotechnol., 37:437-442 (1992); Wang and Yang, “Propionic acid production in glycerol/glucose co-fermentation by Propionibacterium freudenreichii subsp. Shermanii”, Bioresour. Technol., 137:116-123 (June 2013); and Zhang and Yang, “Engineering Propionibacterium acidipropionici for enhanced propionic acid tolerance and fermentation”, Biotechnol. Bioeng., vol. 104, no. 4, pp. 766-773 (Nov. 1, 2009). Additional reduced biobased substrates, for example, glycerol, are taught as useful in some fermentations for improving the redox balance and the yield and selectivity to propionic acid.
The present invention concerns the still further discovery (to those reported in our previous '312 and WO '784 applications) that the same ZnxZryOz mixed oxide catalysts—whether made by the hard template method or by the method of the WO '784 application—are also able, in the presence of hydrogen, to be used to produce several other olefins in addition to isobutene that are either of immediate commercial interest (e.g., propylene) or that can be readily upgraded by known methods to produce other valuable products, starting from a mixture of acetic and propionic acids as may be produced by known fermentation methods for the manufacture of propionic acid or in other ways accessible to those skilled in the art. Examples of the upgradeable olefins include the four-carbon products 1-butene and 2-butene, which can be used to make 1,3-butadiene, and the five-carbon products 2-methyl-1-butene and 2-methyl-2-butene, which can be used to make isoprene. Still other commercially interesting permutations will be apparent to those skilled in the art on consideration of the following summary and detailed description, for making products with biobased organic content that have historically been made exclusively from non-renewable resources.